Polymer matrix composites containing organic resins and reinforcing materials are known in the art for fire resistance applications. For example, Kim et al. Thermal and Flammability Properties ofPoly(p-phenylene-benzobisoxazole), Journal of Fire Sciences, vol. 11, pp. 296-307, 1993 disclose a composite of poly(p-phenylene-benzobisoxazole) (PBO) and carbon fibers. The composite had peak heat release rates of 0 under a heat flux of 50 kW/sq. m; 100 under a heat flux of 75 kW/sq. m; and 153 under a heat flux of 100 kW/sq. m. However, PBO begins to thermally decompose at 660.degree. C.
Sastri et al. Flammability Characteristics ofPhthalonitrile Composites, 42.sup.42 nd International SAMPE Symposium pp. 1032-1038, 1997 disclose a composite comprising phthalonitrile polymer reinforced with glass fabric. The composite has a peak heat release rate of 106 kW/sq. m when exposed to 100 kW/sq. m heat flux. However, char yield of the phthalonitrile resins was 65 to 70 wt % upon pyrolysis to 1000.degree. C.
When composites with silicone resins burn, they typically have a lower heat release rate and lower yields of carbon monoxide, and smoke than composites made with organic polymers.
For example, in Development of Silicone Resins for use in Fabricating Low Flammability Composite Materials, Proc. 42 Int. SAMPE, vol. 42, page 1355, 1997; Chao et al. disclose silicone resins comprised of the units PhSiO.sub.3/2 and ViMe.sub.2 SiO.sub.1/2 or MeSiO.sub.1/2 and ViMe.sub.2 SiO.sub.1/2 (where Ph represents a phenyl group, Vi represents a vinyl group, and Me represents a methyl group). Composites made from these resins and various fillers had lower smoke and carbon monoxide yields as compared to composites made with organic resins. However, these composites still had unacceptably high peak heat release rates (up to 150 kW/sq. m) when exposed to an incident heat flux of 50 kW/sq. m.
Russian Patent SU1941629 assigned to Vargina R A discloses a carbon fiber reinforced press molding obtained from a polymethylsilsesquioxane, polydimethyl methyl phenyl siloxane, and a hydride catalyst. The molding resists thermal oxidation and has good physico-mechanical properties.
U.S. Pat. No. 5,552,466 issued on Sep. 3, 1996, to Beckley et al. discloses a silicone composite with high temperature resistance. The composite is made from a blend of at least one silsesquioxane polymer with a viscosity of at least 500,000 mPa s at 25.degree. C. and at least one polydiorganosiloxane component with a viscosity of 10 to 1,000 mPa s at 25.degree. C. However, no composites are known in the art using the unblended methylsilsesquioxane resin as the matrix.
Therefore, it is an object of this invention to provide a polymer matrix composite with a methylsilsesquioxane resin that has high char yield and retains much of its mechanical strength after burning. Another object of this invention is to provide a method for fabricating the composite.